In a 6- to 8-quart pan, melt butter over medium heat.
Add onions, garlic, and parsley; cook, stirring often, until onions are soft.
Add broth, water, wine, bay leaf, thyme, and rosemary.
Cover and simmer for about 15 minutes.
Rinse salmon, pat dry, and cut into chunks.
Add salmon, clams, and crab to broth.
Cover and simmer gently until clams pop open and salmon flakes readily when prodded with a fork, 10 to 15 minutes Ladle broth and some of each seafood into large soup bowls.